<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      color: red;
      /* font-size: 30px; */
      /* 相对于自身的字体(父元素的字体) */
      /* 16*2=32px */
      font-size: 2em;
    }
  </style>
</head>

<body>
  <div class="box">
    box本身的内容
    <p>我是p元素</p>
  </div>
</body>

</html>